1. Field of the Invention
The present invention relates to an optical disk device for recording, over-writing, and reproducing a signal onto or from a track of an optical disk using an optical spot formed by focusing an optical beam of a semiconductor laser, and more specifically, to an optical disk device that performs test recording at a specified region to detect a recording power and an erasing power of a recording start point before recording in a user region and setting a final recording power and erasing power from the recording start point to enhance recording/reproducing characteristics of signals in the user region.
2. Discussion of the Prior Art
Recently, re-writable optical disks such as magneto-optical and phase change media have been practically used. With phase change media, recording, erasing, and over-writing are performed by thermal recording by light. However, recording margin on an optical output basis is generally small, namely, about 20% to 40%. As for a magneto-optical disk, to realize over-writing with an optical disk having a multi-layered recording media, a second power must be set by adding the optical output to an additional recording power. The same optical output as in the phase change type of optical disk is needed.
When a recording media comprises multiple layers, recording margin decreases compared to conventional magneto-optical disks. When recording bit length is shortened or bit edge recording or land/groove recording systems are used to achieve high density recording, the recording margin is usually less than 20%. This results in setting difficulty for the most suitable recording power to ensure an appropriate recording margin for the system.
In addition to the fundamental narrowness of recording margin, the appropriate recording power changes according to the temperature characteristics and with time. Therefore, fixed recording power determined at the factory may drift from the most appropriate recording power.
To solve this problem, before recording in a particular user region, a test is performed in a specified test region to detect the recording power around the recording start point to set the recording power.
A block diagram of a conventional optical disk device for setting a recording power is described with reference to FIG. 44. Element 1 is an optical disk, 2 is a disk motor for rotating optical disk 1, 3 is an optical head for recording/reproducing a signal onto optical disk 1, 4 is a semiconductor laser used as an optical beam light source, 5 is an optical beam emitted from semiconductor laser 4, 6 is a photodetector receiving a light reflected from optical disk 1 by way of divided detectors, and 7 is a pre-amplifier, digitizer to process the divided signals of photodetector 6 to generate a reproduced signal or a servo signal or to digitize the reproduced signal. Element 8 is an error detection circuit for detecting a bit error or byte error of the reproduced signal. Hereafter, bit error rate or byte error rate is abbreviated as BER. Error judging circuit 9 is used for (i) determining whether the reproduced signal is under an allowable BER value by comparing a threshold level TH, which indicates the allowable BER, to the BER of the reproduced signal, and (ii) for outputting the result.
An optical output control circuit 10 sets an optical output of semiconductor laser 4 at a recording power determined by recording power data DT during the period recording gate GT is on and modulates the output according to a recording signal, or write data WTDT. Recording start point detection circuit 11, after performing recording in a specified test region, changes the setting of the recording power to a recording power that is within an allowable BER value detected by error judging circuit 9.
When the BER is within a predetermined allowed value, recording power Pbt is output as the recording start point to power setting circuit 12. Power setting circuit 12 multiplies recording start point Pbt by a specific constant to set recording power Pst. Actual recording in a user region is performed by recording power Pst. The action for setting recording power is illustrated referring to the flow chart in FIG. 45. First, an optical head seeks a test region other than a user region. An optical output for recording is set at an initial value. The initial value is set at a lower recording power than ordinary recording start points, and accordingly, BER at the initial value is almost certainly higher than the specific allowed value TH. Next, after recording one time by the previously set recording power, the recorded information is reproduced to detect an error rate. Error judging circuit 9 compares allowed value TH and the reproduced BER. The initial value of the first recording power is set low, so BER is high and the judgment result is "NO". When "NO", the track address is incremented by one to the next track and the recording power is increased by a predetermined increment +dP. Recording is performed one time by a newly set recording power and its error is again detected. If the error is improved by increasing recording power by +dP, the judgement result by the error detection circuit 9 is changed to "YES". A "YES" judgement means that recording power Pbt at recording start point is detected. Recording power is then determined by multiplying the recording start point Pbt by a specific constant 1.3 and actual recording power in the user region is performed.
Referring to FIG. 46, the relationship between recording start point Pbt and recording power Pst is illustrated. In FIG. 46, the abscissa shows recording powers, and the ordinate shows BER. As recording power increases from P1 to P4, it can be seen that BER drops below allowed value TH at P4=Pbt. Generally, in optical disk devices, recording power Pst is set by multiplying recording start point Pbt by a specific constant "a". This constant typically includes some margin. When the margin is set at 30% Pst=(1.3)(Pbt). The margin changes according to the width of recording margin of the media and the margins of various parameters of the optical disk device. However, with conventional detecting methods for a recording start point, recording start points may change, and as a result, recording characteristics of the recording power are not optimized.
FIG. 47 illustrates that the recording start point Pbt can change. In FIG. 47, the abscissa shows recording powers and the ordinate shows BER. The plots show three cases on the media of the same optical disk where the history of use differs. Generally, recording power around the recording start point is small and a stable recording characteristic is rarely obtained. Moreover, when the recording media is subjected to relatively larger recording power, sufficient initializing or erasing is not achieved and recording start points vary as shown in FIG. 47. In Case 1 wherein the recording media is relatively clean and initialized sufficiently, recording start point Pbt1 is detected at P2. On the other hand in Case 3 where the recording media is not initialized, sufficiently erased or was subject to a large recording power in the past, recording start point Pbt3 is detected at P5.
As described above, the conventional method has the problem that the recording start point varies largely according to the condition of the recording media.
With over-writable phase change disks, recording power and erasing power of the optical output must be set as shown in FIG. 48. Setting the two optical outputs precisely and efficiently so as to obtain optimal recording characteristics is difficult using conventional methods.
In an actual optical disk, when linear velocity varies, recording sensitivities in the inside radius track and the outside radius track are different. Linear velocity increases as the track moves to the outside and larger linear velocity requires larger recording power as shown in FIG. 49. Therefore, even if the recording power is determined at a test region outside the user region, different recording power must be set in the user region depending on the track used. Thus, precise setting of the recording power in the user region according to the recording power in the test region cannot be solved using conventional methods.